Various systems are available and used to manufacture sheets of paper and other paper products. The sheets of paper being manufactured often have multiple properties that are monitored and controlled during the manufacturing process. With the standard approach to papermaking machine direction (MD) controls, controlled variables, such as basis weight or dry weight of the paper and the ash content of the paper, are measured at the reel and controlled by adjustment of manipulated variables, such as stock flow to the machine and filler addition to the stock. The control of these or other sheet properties in a sheet-making machine is typically concerned with keeping the sheet properties as close as possible to target or desired values.
In the manufacturing process, if there is a sheet break that prevents the paper sheet from reaching the reel scanner, or if the reel scanner malfunctions, the controller loses measurements and the MD controls can no longer be used. During the interim when measurements are not available and the MD controls are off, process changes may occur that move the controlled variables away from, their desired operating points. Subsequently when the sheet is re-threaded, through the papermaking machine and is put back on the reel and/or scanner measurements resume, production is interrupted. While the controller brings these variables back, to target for a period of time after the rethreading, the paper sheet produced may not be usable or saleable. This is because the break in the paper sheet often disturbs or interferes with the control of the sheet-making machine, so the paper sheet produced after the break typically has sheet properties that are not near the target or desired values. As a result, the sheet-making machine often, needs to be operated until the disturbances earned by the break are eliminated and the sheet properties return to or near the target or desired values. This results in a loss of both time and materials. What is needed is a means of keeping the controlled variables close to target even when they cannot be measured.